The influence of an ITER-like wall on disruptions at JET

In order to preserve the integrity of large tokamaks such as ITER, the number of disruptions has to be limited. JET has operated previously with a low frequency of disruptions (i.e., disruption rate) of 3.4% [P. C. de Vries et al., Nucl. Fusion 51, 053018 (2011)]. The start of operations with the new full-metal ITER-like wall at JET showed a marked rise in the disruption rate to 10%. A full survey was carried out to identify the root causes, the chain-of-events and classifying each disruption, similar to a previous analysis for carbon-wall operations. It showed the improvements made to avoid various disruption classes, but also indicated those disruption types responsible for the enhanced disruption rate. The latter can be mainly attributed to disruptions due to too high core radiation but also due to density control issues and error field locked modes. Detailed technical and physics understanding of disruption causes is essential for devising optimized strategies to avoid or mitigate these events.

[1]  J. Stober,et al.  Influence of the heating profile on impurity transport in ASDEX Upgrade , 2003 .

[2]  Michela Gelfusa,et al.  Clustering based on the geodesic distance on Gaussian manifolds for the automatic classification of disruptions , 2013 .

[3]  J. Vega,et al.  Results of the JET real-time disruption predictor in the ITER-like wall campaigns , 2012 .

[4]  M. Sugihara,et al.  Disruption scenarios, their mitigation and operation window in ITER , 2007 .

[5]  F C Schuller,et al.  Disruptions in tokamaks , 1995 .

[6]  M. N. A. Beurskens,et al.  JET ITER-like wall—overview and experimental programme , 2011 .

[7]  J. Contributors,et al.  Survey of disruption causes at JET , 2011 .

[8]  Gianmaria De Tommasi,et al.  First plasma operation of the enhanced JET vertical stabilisation system , 2011 .

[9]  Jet Efda Contributors,et al.  First operation with the JET International Thermonuclear Experimental Reactor-like wall , 2013 .

[10]  M. Lehnen,et al.  Disruption heat loads and their mitigation in JET with the ITER-like wall , 2013 .

[11]  Jet Efda Contributors,et al.  Observations on the W-transport in the core plasma of JET and ASDEX Upgrade , 2013 .

[12]  J. Contributors,et al.  Metal impurity transport control in JET H-mode plasmas with central ion cyclotron radiofrequency power injection , 2011 .

[13]  G. G. Stokes.  "J." , 1890, The New Yale Book of Quotations.

[14]  R. E. Bell,et al.  Disruptions, disruptivity and safer operating windows in the high-β spherical torus NSTX , 2012 .

[15]  A. Fanni,et al.  Manifold learning to interpret JET high-dimensional operational space , 2013 .

[16]  David Ward,et al.  Impurity influx model of fast tokamak disruptions , 1992 .

[17]  J. Contributors,et al.  Statistical analysis of disruptions in JET , 2009 .

[18]  Jet Efda Contributors,et al.  Use of the disruption mitigation valve in closed loop for routine protection at JET , 2013 .

[19]  J. Contributors,et al.  Impact of the ITER-like wall on divertor detachment and on the density limit in the JET tokamak , 2013 .

[20]  K. F. Mast,et al.  Disruptions in JET , 1989 .

[21]  E. Joffrin,et al.  The CRONOS suite of codes for integrated tokamak modelling , 2010 .

[22]  M. Lehnen,et al.  Impact and mitigation of disruptions with the ITER-like wall in JET , 2013 .

[23]  J. Contributors,et al.  Transient impurity events in JET with the new ITER-like wall , 2014 .

[24]  Miss A.O. Penney.  (b) , 1974, The New Yale Book of Quotations.

[25]  J. Manickam,et al.  Chapter 3: MHD stability, operational limits and disruptions , 2007 .

[26]  R. Neu,et al.  The impact of the ITER-like wall at JET on disruptions , 2012 .

[27]  C. D. Challis,et al.  Scientific preparation for future D-T campaigns at JET in support of ITER , 2011 .